The goal of this research is to determine how leukemic cells (in acute myeloid leukemia induced by avian myeloblastosis virus) acquire a growth advantage over normal hemopoietic stem cells. The hypothesis is that a growth factor for the leukemic cells is produced in abnormally high amounts in the animal with leukemia (in addition to the production of growth inhibitors which we have shown to act preferentially on normal hematopoietic progenitors). The plan is to identify factors (in the leukemic animal) which influence growth and differentiation of hemopoietic cells and to determine the role that these factors have on the growth and differentiation of leukemic cells. The factors are assayed by the effect they have on the in vitro clonal growth of normal and leukemic hemopoietic cells in semisolid medium. The long-term clinical objective is to determine if the restoration of normal levels of these hormone-like factors would be therapeutic. The specific aims for the next year are (1)\to purify the growth factor which acts on leukemic cells and (2)\to determine the potential of the leukemic cell to differentiate along different hematopoietic pathways.